Hi Hesham,
You got 3 options
Widgets: use JavaScript, or typescript ; visual and interactive client side components https://docs.mendix.com/apidocs-mxsdk/apidocs/pluggable-widgets#1-introduction
JavaScript Action: Javascript ES6, Extend client side logic; https://docs.mendix.com/refguide/javascript-actions
Java Actions: Java, Extend server side logichttps://docs.mendix.com/refguide/java-actions#1-introduction
Cheers, Andries
Hello, welcome.
On the academy section, there are some training paths to get a base knowledge what you can expect of Mendix and how Mendix is working. I would suggest to take a look at it, maybe it can help you answering your questions.